The number of acidic radicals which give colourless gas or fumes when treated with dil. HCl on heating isS2–, , , CH3COO–, , , Cl–, Br–

The acidic radicals that give colorless gas or fumes when treated with dilute HCl on heating are S2-, CH3COO-, Cl-, and Br-.

Here's the step-by-step explanation:

1. S2- (Sulphide ion): When treated with dilute HCl, it forms Hydrogen Sulphide (H2S), which is a colorless gas.

2. CH3COO- (Acetate ion): When treated with dilute HCl, it forms Acetic acid and water. However, it does not produce any colorless gas or fumes.

3. Cl- (Chloride ion): When treated with dilute HCl, it does not react because HCl is already a compound of Hydrogen and Chloride. Therefore, it does not produce any colorless gas or fumes.

4. Br- (Bromide ion): When treated with dilute HCl, it forms Hydrogen Bromide (HBr), which is a colorless gas.

So, the acidic radicals that give colorless gas or fumes when treated with dilute HCl on heating are S2- and Br-.